Manufactured fuel logs and pellets for fireplaces and stoves are well known as an alternative heat source and for aesthetic enjoyment. Such fuels are selected for convenience, efficiency and cost advantages. The higher burn rate, longer burn time, and higher energy density make processed solid fuel a more convenient alternative over natural wood. Furthermore, wood has more valuable uses, and is accordingly more costly. The desire to reduce wood consumption to a sustainable rate, and to reduce the significant deforestation currently occurring, adds additional motivation to find an alternative fuel source. Finally, decreasing landfill capacities have generated searches for alternative uses of waste byproducts.
In a study by David A. Tillman, The Combustion of Solid Fuels and Wastes published in 1991, the combustion of solid fuels and wastes (including coffee waste) is suggested as potentially economical in raising process energy, generating electricity, and reducing the volume of municipal waste in landfills. The combustion of solid fuel particles--such as biomass, fossil fuels and municipal refuse--in an industrial furnace, boiler or kiln at high rates is investigated. The many advantages of coffee as a fuel source are not apparent in these teachings. Furthermore, no proposal is made for the production of processed solid fuels or domestically combustible fuels.
Prior art manufactured logs and pellets for domestic use have not been entirely satisfactory either in burn characteristics or in costs. A discussion of prior art illuminates the advantages offered by the present invention. The main advantages of processed fire-logs generally include long burn time, easy lighting characteristics, and convenience of use for preparation or maintenance of the fire. As a replacement for natural wood fires, processed logs offer the convenience of not having to stoke the fire to ensure a consistent flame. One log typically bums between 3 to 4 hours, depending on the size of log.
However, these advantages are not unqualified. In order to achieve both a substantial flame and a quick ignition time, a significant amount of wax is used. The high combustion rate, in combination with limited air supply, typically results in incomplete combustion, which in turn leads to a buildup of soot and creosote in the flue. This incomplete combustion is further intensified by the low infiltration rates common in new home construction. Repeated use of such prior art fuel logs, represents a fire hazard. Indeed, due to the seriousness of this problem, insurance companies recommend that consumers alternate between the use of artificial fire-logs and natural wood fires, in addition to frequent cleaning of combustion apparatus.
Not only does the excessive use of wax represent a safety hazard due to the build-up of soot, but it means that the consumer is provided with an aesthetically less pleasing product than natural wood fires. While the substantial use of wax promotes faster ignition, the flame height for the later stages of combustion is significantly lower than in the beginning. Hence, it is difficult for the user to enjoy a flame comparable to a well-maintained natural wood fire. It is desired to provide a solid fuel which incorporates less wax, yet still retains high energy burn characteristics.
In order to improve ignition time, without affecting the combustion properties of the entire log, an "ignition strip" is disclosed in U.S. Pat. No. 4,043,765 issued to Tanner in 1977. Given the high combustion rates associated with a high wax content, this would be a preferable approach to improving ignition time. However, a high proportion of wax throughout the product is still required to maintain a high burn rate following ignition.
A synthetic log is disclosed in U.S. Pat. No. 5,393,310 issued to Wollen in 1995, which incorporates a large proportion of waste products, namely grass clippings and leaves. It is an object of this prior invention to use the composition to reduce yard waste in the waste stream while providing a burnable fuel. Leaves and grass clippings, however, do not provide a satisfactory fuel source, and even with the addition of significant amounts of paraffin wax, such logs have a low calorific value. It is suggested that the grass clippings be incorporated directly from the lawn without further processing. This also means that a higher moisture content will be present to hinder burning.
In response to pressures on the supply of petroleum waxes, and hence the increasing cost, U.S. Pat. No. 4,326,854 issued in 1982 to Tanner discloses the use of a liquid combustible by-product with cellulosic and ligno-cellulosic materials in a synthetic fire log. In this disclosure a skeleton of solid burnable material such as sawdust or other material such as peanut shell fines, cocoa bean shell fines, coconut shell or walnut shell fines, bagasse or paper pulp, is incorporated at between 25% and 70% by weight with a binder comprising a liquid combustible byproduct, which is solidified by either polymerization or neutralization with the addition of various chemicals. The preferred liquid binder is molasses. As one of many examples, Tanner tested a composition containing 60 parts (by weight) vegetable pitch, 6 parts oleic acid, 3 parts caustic soda, and 37 parts coffee grounds. As the major portion of the composition is liquid combustible byproduct, advantages from burning coffee of cleaner burn and higher energy yield are not observable from Tanners results.
Pellet fuels contain fewer additives than manufactured logs, commonly being formed of wood and other ligno-cellulosic material, such as bark compressed under high pressure. Pellet fuel is attractive for burning in stoves for heating purposes, since a large quantity can be charged in a hopper for continuous release as needed. The uniform size of the pellets and the controlled feed rate results in more efficient combustion than larger solid fuels. Because a pellet stove may be self-feeding, and hence burning for many hours continuously, a clean burning fuel which produces less ash is desired. However, as a heat source, a fuel with a higher energy density is also desired.
Pellets are burned over a grate through which remaining ash is removed. It is important that the pellets retain their shape during handling and combustion without crumbling, which would add fines to the feed stream. Fines of unburned fuel can drop through the grate where they may be ignited by hot ash. This is not only a waste of fuel, but also a safety problem. Wood-based biomass and sawdust is very irregular in size, due to the process in which it is created. Therefore, it must be ground to the correct consistency prior to being pelletized, adding a significant amount of processing costs.
Coffee, in the form of spent grounds, is a very attractive fuel source for manufactured logs and pellets. Coffee contains approximately 25% higher energy potential than dry hardwood. Used coffee also has a highly uniform particle size. Currently no further use is available for spent coffee. Thus the use of coffee as a fuel source is energy efficient, inexpensive and diverts waste from landfill. By utilizing the desirable characteristics inherent to coffee grounds, a premium solid fuel can be produced according to the present invention without large quantities of added wax. This fuel offers efficiency, cost, environmental, safety and aesthetic advantages over existing processed solid fuels.